Abstract

The CGM is a critical reservoir of baryons for galaxies, as well as an interface at which pristine inflowing gas and outflows interact. Despite its long-known importance to the baryon cycle and evolution of galaxies, spatially resolved studies of the CGM have been challenging observationally, due particularly to the low density, diffuse, and multiphase nature of the gas. Here, I will present  the design of and early results from the Dragonfly Spectral Line Mapper — a novel, telephoto array-based instrument equipped with ultranarrowband (0.8 nm) tunable filters, which can target Halpha, [NII], and [OIII] for gas in the local universe with velocities < 4000 km/s. The instrumental design features a large field of view (1 deg x 1 deg) and will reach depths of 10^-20 erg/s/cm2/arcsec2 — allowing us to directly image the extent and structure of warm (10^4 K) gas in the CGM of nearby galaxies out to the virial radius. Early prototypes of the (in construction) instrument have already produced new results, including a new tidal dwarf galaxy progenitor and large shell of ionized gas around the nearby starburst M82. I will also discuss comparisons to the TNG50 simulations at our expected depths, and what we might learn from comparing simulations to these observations.